Fuel control system and method of operating the same

ABSTRACT

A fuel control system for a main burner having a pilot burner therefor and a thermostatically operated control device for directing fuel from a source to the pilot burner upon the demand of fuel for the main burner whereby a safety valve will direct fuel from the source to the main burner only upon the detection of a certain flame at the pilot burner. An electrical ignition unit is provided for igniting fuel issuing from the pilot burner. A condition responsive electrical switch is provided for rendering the ignition unit operable when fuel is directed to the pilot burner upon a demand for fuel for the main burner by the condition responsive switch being responsive to the fuel flow to the pilot burner. The condition responsive switch also renders the ignition unit inoperable when the safety valve is directing fuel from the source to the main burner upon a detection thereby of the certain flame at the pilot burner by the condition responsive switch being responsive to the fuel flow to the main burner.

United States Patent Branson 51 Se t. :"16, 1975 [75] Inventor: CharlesD. Branson, Greensburg,

[73] Assignee: Robertshaw Controls Company,

Richmond, Va.

[22] Filed: Feb. 25, 1974 [21] Appl. No.: 445,258

[52] US. Cl. 431/58; 236/15 A; 251/46; 431/61; 431/89 [51] lnt. Cl. F23Q9/08 [58] Field of Search 431/44, 46, 72, 74, 58; 236/15 A; 251/46;200/819 A [56] References Cited UNITED STATES PATENTS 2.625.216 l/1953Strobel 431/44 2,652,110 9/1953 Main 431/46 3.575.542 4/1971 Branson etal 236/15 A Primary Examiner-William F. OlDea Assistant Examiner lamesC. Yeung Attorney, Agent, or Firm-Candor, Candor & Tassone ABSTRACT Afuel control system for a main burner having a pilot burner therefor anda thermostatically operated control device for directing fuel from asource to the pilot burner upon the demand of fuel for the main burnerwhereby a safety valve will direct fuel from the source to the mainburner only upon the detection of a certain flame at the pilot burner.An electrical ignition unit is provided for igniting fuel issuing fromthe pilot burner. A condition responsive electrical switch is providedfor rendering the ignition unit operable when fuel is directed to thepilot burner upon a demand for fuel for the main burner by the conditionresponsive switch being responsive to the fuel flow to the pilot burner.The condition responsive switch also renders the ignition unitinoperable when the safety valve is directing fuel from the source tothe main burner upon a detection thereby of the certain flame at thepilot burner by the condition responsive switch being responsive to thefuel flow to the main burner.

32 Claims, 2 Drawing Figures 78 L2- y W SHEET 2 OF 2 ATENTEU SEP 1 1975FUEL CONTROL SYSTEM AND METHOD OF OPERATING THE SAME This inventionrelates to an improved fuel control system for a main burner of acooking apparatus or the like as well as to an improved method ofoperating such a fuel control system or the like.

It is well known that fuel control systems for main burner means ofcooking apparatus have been provided wherein each system has a pilotburner means for the main burner means and a thermostatically operatedcontrol device for directing fuel from a source thereof to the pilotburner means upon the demand of fuel for the main burner means whereby asafety valve will direct fuel from the source to the main burner meansonly upon the detection of a certain heater flame means at the pilotburner means. For example, such a system is illustrated and described inthe US. patents to Tyler, US. Pat. No. 3,341,119, to Branson et al., US.Pat. No. 3,367,572 and to Rich] US Pat. No. 3,405,999.

However, it has been found that in such a fuel control system, the pilotburner means is constantly supplied a small standby flow of fuel fromthe fuel source manifold so that a constantly burning small standbyflame exists at the pilot burner means which will either ignite theheater pilot fuel flow from the thermostatically operated control deviceor be expanded into such heater pilot flame means by having the heaterpilot fuel flow added thereto as illustrated and described in theaforementioned U.S. patents whereby the ignition means for such a fuelcontrol system constantly burns fuel at the pilot burner means for themain burner means even though the main burner means is not in use duringlarge periods of time. Accordingly, it is believed that such constantlyburning small standby flame during the nonuse of the main burner meansconstitutes an unnecessary loss of energy.

Therefore, it is a feature of this invention to provide a pilot burnerignition means for such a fuel control system wherein the pilot burnermeans is only rendered operable during a desired cycle of operation ofthe main burner means associated therewith.

In particular, one embodiment of this invention provides an electricalignition means for igniting fuel issuing from a pilot burner means for amain burner means, the fuel issuing from the pilot burner means when athermostatically operated control device directs fuel from a sourcethereof to the pilot burner means upon the sensing of the demand forfuel to issue from the main burner means. Thus, a safety valve willdirect fuel from the fuel source to the main burner means only upon thedetection of a certain heater flame means at the pilot burner means. Acondition responsive electrical switch of this invention is provided forrendering the ignition means operable when fuel is directed to the pilotburner means upon a demand for fuel for the main burner means by thecondition responsive electrical switch being responsive to the fuel flowto the pilot burner means. The condition responsive electrical switchrenders the ignition means operable when the safety valve is directingfuel from the fuel source to the main burner means upon detectionthereby of the certain heater flame means at the pilot burner means bythe condition responsive electrical switch being responsive to the fuelflow to the main burner means.

Such an arrangement of this invention can provide the aforementionedoperation of the electrical ignition means each time the safety valve iscycled between its of and on" conditions to insure that the pilot burnermeans will be ignited when the fuel flow for creating the heater flamemeans is directed thereto by the thermostatically operated controldevice.

Another arrangement of this invention will provide for theaforementioned operation of the electrical ignition means only at thestart of a particular cycle of operation of the main burner meanswhereby a small standby flame will be created at the pilot burner meansafter initial ignition thereof to provide for subsequent ignition of theheater pilot flow during the cyclic operation of the safety valve forthe particular setting of the thermostatic control device.

Therefore, it is an object of this invention to provide an improved fuelcontrol system having one or more of the novel'features set forth orhereinafter shown or described.

Another object of this invention is to provide an improved method ofoperating such a control system or the like.

Other objects, uses and advantages of this invention are apparent from areading of this description which proceeds with reference to theaccompanying drawings forming a part thereof and wherein:

FIG. 1 is a schematic view illustrating one embodiment of the improvedfuel control system of this invention.

FIG. 2 is a view similar to FIG. 1 and illustrates another embodiment ofthis invention.

While the various features of this invention are hereinafter describedand illustrated as being particularly adapted for providing a fuelcontrol system for a cooking apparatus, it is to be understood that thevarious features of this invention can be utilized singly or in anycombination thereof to provide a fuel control system for other apparatusas desired.

Therefore, this invention is not to be limited to only the embodimentsillustrated in the drawings, because the drawings are merely utilized toillustrate one of the wide variety of uses of this invention.

Referring now to FIG. 1, one embodiment of the improved fuel controlsystem of this invention is generally indicated by the reference numeral10 and comprises a main burner means 11 for heating an over 12 of asuitable cooking apparatus 13 to tend to maintain the temperature of theoven 12 at the temperature setting of a selector means 14 of athermostatically operated control device 15 in a manner hereinafterdescribed.

The control device 15 comprises a housing means 16 having a chamber 17therein and an inlet portion 18 leading to the chamber 17 and beingdisposed in fluid communio' ation with a fuel source manifold 19 asillustrated, thc inlet 18 having an on and of valve means 20 thereinadapted to be opened and closed by the selector means 14. In particular,when the selector means 14 is moved to any onl condition thereof, thesame not only opens the valve member 20 to interconnect the fuel supplymanifold 19 with the chamber 17 of the control device 15, but also theselector l4 adjusts the fulcrum point of a pivotally mounted lever 21disposed in the chamber 17 and carrying a valve member 22 on one endthereof for controlling a valve seat 23 and being responsive at theother end thereof to the expansion and contraction of a power element 24having the interior chamber thereof interconnected by a capillary tube25 to a temperature sensing bulb 26 disposed in the oven 12. When theselector 14 is moved to its off position, the same not only closes thevalve 20 to disconnect the fuel supply manifold 19 from the chamber 17,but also the selector moves the lever 21 so that the valve member 22fully closes the valve seat 23 regardless of the expanded or collapsedcondition of the power element 24.

The valve seat 23 of the control device is interconnected by a conduitmeans 27 to a dual rate pilot burner means 28 by a branch conduit 29,the dual rate pilot burner means 28 being of a type similar to the pilotburner means described and illustrated in the aforementioned U.S. patentto Riehl, U.S. Pat. No. 3,405,999.

A bypass passage 30 is also provided in the housing means 16 of thecontrol device 15 to supply a bypass flow of fluid from the chamber 17of the control device 15 into the conduit 27 leading to the dual ratepilot burner means 28 for supplying a standby flow of fuel to the pilotburner means 28 when the valve member is in an open condition and thevalve seat 23 is in a closed condition so that a small standby flame canexist at the pilot burner means 28 in an area not to be detected by aflame sensing bulb 31 of a safety valve 32 that has an outlet 33 thereofinterconnected by a suitable orifice cup 34 to the interior of theburner means 11 and an outlet 35 interconnected by conduit means 36 toan outet 37 of the control device 15. A valve member 38 of the safetyvalve 32 is adapted to open and close a valve seat 39 separating theinlet 35 from the outlet 33 in a manner fully set forth in theaforementioned U.S. patents whereby when the bulb 31 detects a largeheater flame at the end 40 of the dual rate pilot burner means 28created in a manner hereinafter described, a power element 41 of thesafety valve 32 will have expanded in such a manner that the same willoperate a lever and spring arrangement 42 of the safety valve 32 to movethe valve member 38 away from the valve seat 39 and hold the same in anopen condition to interconnect the inlet 35 with the outlet 33 as longas the heater flame means exists at the end 40 of the dual rate pilotburner 28. Thus, fuel is adapted to flow from the chamber 17 of thecontrol device 15 to the main burner means 11 to be ignited by theaforementioned small standby flame and/or the large heater flame at theend 40 of the dual rate pilot burner 28 so as to increase thetemperature in the oven 12 as will be apparent hereinafter.

An electrical ignition unit 43 is disposed adjacent the pilot burnermeans 28 for igniting fuel issuing therefrom when the unit 43 isenergized, the unit 43 being any desired electrically operated ignitionmeans, such as a conventional electrical ignition coil or the like.

In any event, the electrically operated ignition unit 43 has opposedsides 44 and 45 thereof respectively interconnected by leads 46 and 47to oppose sides 48 and 49 of a secondary winding 50 of an electricaltransformer 51 having a primary winding 52. The primary winding 52 ofthe transformer 51 has opposed sides 53 and 54 respectivelyinterconnected to leads 55 and 56.

The lead 55 is interconnected to a power source lead Ll while the otherlead 56 is adapted to be interconnected by a condition responsiveelectrical switch construction of this invention, that is generallyindicated by the reference numeral 57, to a lead 58 that isinterconnected to another power source lead L2 so that when theelectrical switch construction 57 is in a closed condition thereof asillustrated in FIG. 1, electrical current is adapted to flow from thepower source leads L1 and L2 through the primary winding 52 of thetransformer 51 and thereby induce a current flow in the secondarywinding 50 which will electrically operate the ignition unit 43 forigniting any fuel that is issuing from the pilot burner means 28 in amanner hereinafter described. When the electrical switch construction 57is in an open condition, no current flow can be induced in the ignitionmeans 43 whereby the open electrical switch construction 57 renders theignition unit 43 inoperable for a purpose hereinafter described.

The electrical switch construction 57 of this invention comprises ahousing means 59 carrying a pair of flexible diaphragms 60 and 61 thatdivide the housing means 59 into three separate chambers 62, 63 and 64,the chamber 62 being interconnected by a conduit means 65 to the branchconduit means 29 that leads to the pilot burner means 28, the chamber 63being interconnected by a conduit means 66 to the fuel supply manifold19 and the chamber 64 being interconnected by a conduit 67 to the outlet33 of the safety valve 32 downstream from the valve seat 39 thereof fora purpose hereinafter described.

An electrical switch 68 is disposed in the chamber 63 of the switchconstruction 57 and comprises a fixed terminal 69 having a contact 70thereon and a pair of projecting out through an insulating part 71 ofthe housing means 59 to be interconnected to the lead 58. A movablespring switch blade 72 carried by another terminal 73 of theconstruction 57 that has a pair thereof projecting out through anotherinsulating part 74 of the housing 59 to be interconnected to the lead56, the switch blade 72 carrying a contact 75 adapted to cooperate withthe contact 70 and having a natural bias toward the contact 70 forclosing the electrical switch 68. However, the switch blade 72 isinterconnected to a projection 76 on the diaphragm 60 so that movementof the diaphragm 60 to the right in FIG. 1 in a manner hereinafterdescribed will cause movement of the switch blade 72 to the' right toopen the contact 75 away from the contact 70 and thereby terminatecurrent flow through the switch 68 for a purpose hereinafter described.

The diaphragm 61 carries a projection 77 which is not interconnectedwith the switch blade 72 but is adapted to engage against the same andmove the switch blade 72 to the right to open the switch 68 when thediaphragm 61 is moved to the right in a manner hereinafter described,the diaphragm 61 being normally biased to the right by a compressionspring 78 disposed in the chamber 64.

The conduit 29 that leads to the dual rate pilot burner 28 has arestriction 79 therein for a purpose hereinafter described and theconduits 65 and 67 can respectively have restriction means 80 and 81therein adjacent the respective chambers 62 and 64 of the construction57 so that should leaks occur through either or both diaphragms 60 and61, the restriction means 80 and 81 will prevent any adverse amount ofgas to escape from the chamber 63 to the atmosphere through the conduits65 and 67.

Also, an indicator light 82 can have opposed sides 83 and 84 thereofinterconnected respectively by leads 85 and 86 to the leads 56 and 55 sothat the indicator light 82 will indicate to the operator when currentis flowing through the transformer 51 and, thus, is operating theigniting unit 43 for a purpose hereinafter described.

The operation of the control system will now be described.

When the control system 10 is disposed in an of condition by theselector 14 being disposed in its off position, the valve 20 in thecontrol device 15 is disposed in a closed position so that no fuel canflow through the control device 15 to the safety valve means 32 andpilot burner means 28 whereby the chambers 62 and 64 of the electricallyoperated switch construction 57 are at atmospheric conditions. Thus,since the chamber 63 of the device 57 is interconnected to the fuelsource manifold 19, the fuel pressure in the chamber 63 actsrespectively on the diaphragms 61 and 60 to move the same respectivelyto the left and to the right in FIG. 1 in such a manner that thediaphragm 61 compresses the spring 78 so that the bumper 77 thereof isout of contact with the switch blade 72. The diaphragm 60 is moved tothe right in such a manner that the natural bias of the switch blade 72is overcome by the diaphragm 60 being moved to the right so that theswitch blade 72 is held out of contact with the fixed contact 70 so thatno electrical current can flow through the device 57 to cause operationof the ignition means 43.

However, once the operator turns the selector means 14 to a desired on"condition thereof, such as-a 350 F setting for the oven 12, suchmovement of the selector means 14 to such on condition not only opensthe valve means to interconnect the fuel supply manifold 19 to thechamber 17 of the control device 15, but

also the selector means 14 sets the fulcrum point for the lever 21 sothat the valve member 22 is moved immediately to its fully opencondition relative to the valve seat 23 as the bulb 26 is at roomtemperature and thereby causing the power element 24 to be in itscompletely collapsed condition and thereby demanding full heat from theburner means 11. Thus, a large amount of fuel from the chamber 17 passesthrough the fully opened valve seat 23 to the dual rate pilot burnermeans 28. However, because of the restriction 79 in the conduit 29upstream from the dual rate pilot burner 28, sufficient back pressure offuel is created in the conduit 65 and the chamber 62 of the device 57 sothat the same acting on the right side of the diaphragm 60 incombination with the natural force of the spring blade 72 overcomes theforce of the fluid in the chamber 63 acting on the left side of thediaphragm 60 and moves the switch blade 72 into contact with the fixedcontact 70 and thereby operates the transformer 51 so that theelectrically operated ignition unit 43 is likewise operated to ignitefuel now issuing from the pilot burner means 28.

Since the fuel now issuing from the pilot burner means 28 is the largeflow provided by the fully opened valve seat 23, a large heater flame iscreated at the pilot burner means 28 which is detected by the bulb 31which causes the safety valve 32 to open its valve member 38 away fromthe valve seat 39 and interconnect the flow of fuel into the chamber 17of the control de vice 15 to the main burner means 11 so that the samecan issue from the main burner means 11 and be ignited by the pilotburner means 28.

When the valve member 38 of the safety valve means 32 opens to directfuel to the main burner means 11,

such flow of fuel through the open valve seat 39 of the safety valvemeans 32 is transmitted by the conduit 67 to the chamber 64 of theelectrical switch construction 57 and the same in combination with theforce of the compression spring 78 acts on the diaphragm 61 to move thediaphragm to the right and, through the bumper means 77 thereof movesthe switch blade 72 and diaphragm 60 to the right so that the switchblade 72 is out of contact with the contact 70. Thus, the electricalswitch construction 57 now has its switch 68 disposed in an opencondition whereby the ignition unit 43 is rendered inoperative duringthe flow of fuel through the opened safety valve 32.

In this manner, the burner means 11 continue to operate as set forthabove until the temperature sensing bulb 26 senses that the temperaturein the oven 12 is now at or slightly above the desired temperaturesetting of the selector means 14, which, in the above example, is 350 F.At this time the power element 24 has so expanded that the same hascaused the valve member 22 to close against the valve seat 23 andthereby terminate the large flow of fuel to the pilot burner means 28whereby the large heater flame at the end 40 of the pilot burner means28 now ceases to exist even though the bypass passage 30 is stilldirecting a sufficient bypass fuel flow into the conduit 27 to support asmall standby flame at the pilot burner means 28 which will not bedetected by the bulb 31. Thus, since the bulb 31 now detects that nolarger heater flame exist at end 40 of the pilot burner means 28, thesafety valve 32 closes its valve member 38 against the valve seat 39 toterminate the flow of fuel to the main burner means 11.

At this time, the chambers 62 and 64 of the switch construction 57 bleeddown to substantially atmospheric condition, but the switch 68 remainsopen as the fuel pressure in the chamber 63 holds the diaphragm to theright so that the switch blade 72 cannot contact the contact 70 as thesmall standby flow of fuel through the bypass passage 30 is notsufficient to build up sufficient pressure in the chamber 62 to overcomethe pressure in chamber 63.

Subsequently, when the temperature in the oven 12 falls slightly belowthe selected temperature of 350 F, the power element 24 has collapsedonly slightly so that the valve member 22 only is moved a slightdistance away from the valve seat 23 so that a relatively small flow ofadditional fuel now passes through the open valve seat 23 in comparisonwith the amount when the oven 12 was at a temperature greatly below thetemperature setting of the selector means 14, as upon the initialoperation of the control device 15, so that while the flow of fuel thatis now permitted to pass through the open valve seat 23 is sufficient tocreate a large heater flame means at the end 40 of the pilot burnermeans 28 to be detected by the detector 31, such flow of fuel is notsufficiently great to cause a build up of pressure in the chamber 62 toovercome the force of the pressure in the chamber 63 that tends to holdthe diaphragm 60 and switch blade 72 to the right. Thus, the switch 68remains in an open condition so that upon this opening of the valvemember 22 away from the valve seat 23 of the control device 15, theelectrical operated ignition unit 43 is not operated and the increasedflow of fuel to the pilot burner means 28 through the open valve seat 23is caused to burn by the previously described standby flame at the pilotburner means 28 so that the safety valve 32 can be opened in the mannerpreviously described to direct fuel to the main burner means 11 to beignited by the dual rate pilot burner means 28 to tend to heat up theoven 12 to the selected temperature.

Therefore, it can be seen that on subsequent openings and closings ofthe valve member 22 to cause subsequent on-off operation of the mainburner means 11 to tend to maintain the temperature in the oven atselected temperature, the flow of fuel through the heater pilot valveseat 23 is not sufficient to cause the electrically operated switchconstruction 57 to have the switch 68 thereof closed as when the samewas closed by the initial opening of the valve seat 23 upon the start,of the operation of the control system in the manner previouslydescribed.

When it is desired to terminate the previously described operation ofthe oven 12, the operator turns the selector means 14 to the ofcondition thereof whereby the valve member 20 is moved to a closedposition and the valve member 22 is moved to a closed position. Since aheater flame can no longer exist at the pilot burner means 28, thesafety valve 32 closes and since no fuel can flow into the chamber 17 ofthe control device 15, the standby pilot flow of fuel through the bypasspassage 30 is terminated so that no flame will exist at the pilot burnermeans 28. Also, the chambers 62 and 64 of the electrical switchconstruction 57 return to atmospheric condition so that the pressure inthe chamber 63 in the manifold 19 moves the diaphragms 61 and 60 in themanner previously described so that the switch 68 is held in an opencondition during the entire time that the control system 10 is in theoff condition.

Thus, it can be seen that the control system 10 of this inventionprevents any standing pilot flame to exit at the pilot burner means 28during the nonuse of the oven 12 and when it is desired to utilize theoven 12, the electrically operated ignition unit 43 is only operated atthe start of the cycle of operation of the oven 12 as a standby pilotflame is created at the pilot burner means 28 for permitting cylicaloperation of the safety valve means 32 and, thus, the burner means 11during the operation of the oven 12 in the manner previously described.

However, it may be desired to have electrically operated ignition unit43 be operated each time the safety valve means 32 is cycled between itsclosed and open position and therefore another control system of thisinvention can be utilized and is generally indicated by the referencenumeral 10A in FIG. 2 where parts ofthe system 10A substantiallyidentical to parts of the system 10 previously described are indicatedby like reference numerals followed by the reference letter Asillustrated in'FIG. 2, the main burner means 11A, pilot burner means28A, safety valve means 32A and control device A are substantiallyidentical to like parts of the system 10 previously described but adifferent electrical switch construction is provided which is generallyindicated by the reference numeral 57A in FIG. 2, and comprises only onediaphragm 61A for separating the housing means 59A into two chambers 64Aand 87. Further, the electrically operated ignition unit 43A for thepilot burner means 28A has the opposed sides 44A and 45A thereofrespectively interconnected to leads 88 and 89 with the lead 88 beingdirectly interconnected to the power source lead L2 while the lead 89 isadapted to be interconnected through the electrical switch construction57A to a lead 90 that is interconnected to a power source lead L1.

The electrical switch 68A that is disposed in the chamber 87 of theswitch construction 57A has the blade 72A thereof provided with a normalbias in a direction to close the same against the fixed contact 7 0A.However, the compression spring 78A disposed in the chamber 64A andacting on the diaphragm 61A normally tends to move the bumper 77A of thediaphragm 61A upwardly to hold the switch blade 72A in the opencondition illustrated in FIG. 2.

If desired, the indicator light 82A can have the leads 85A and 86Athereof respectively interconnected to the leads 88 and 89 so that thelight 82A will turn on whenever the switch 68A is closed to indicatethat the electrical ignition unit 43A is being operated.

The operation of the control system 10A will now be described.

When the selector means 14A of the control device 15A is in the ofposition so that the valve means 20A and 22A are closed, the chambers 87and 64A of the electrical construction 57A are at atmospheric conditionsso that the force of the compression spring 78A has moved the diaphragm61A upwardly as illustrated in FIG. 2 to hold the switch 68A in the opencondition illustrated whereby the ignition means 43A cannot be operatedand no fuel is permitted to pass from the chamber 17A of the controldevice 15A to the pilot burner means 28A so that no flame exists at thepilot burner means 28A.

However, when the operator turns the selector means 14A to a desiredtemperature setting for the oven 12A, such on position of the selectormeans 14A not only opens the valve means 20A, but also the selectormeans 14A moves the fulcrum point for the lever 21A to the selectedtemperature setting position thereof and since the oven 12A is in a coldcondition, the valve member 22A is moved fully away from the valve seat23A in the manner illustrated in FIG. 2 so that fuel is now adapted toflow to the pilot burner means 28A as well as to the chamber 87 of theelectrical switch construction 57A. The presssure of the full fuel flowin the chamber 87 acts on the diaphragm 61A and overcomes the force ofthe compression spring 78A to move the diaphragm 61A downwardly in FIG.2 whereby the switch blade 72A is adapted to follow such downwardmovement through the natural resiliency thereof to close the switch 68Aand thereby interconnect the ignition unit 43A across the power sourceleads L1 and L2 so that the unit 43A can ignite the fuel now issuingfrom the pilot burner means 28A. Thus, a large heater flame now existsat the end 40A of the pilot burner means 28A to be detected by thedetector 31A so that the safety valve means 32A can be moved to an opencondition thereof.

The opening of the safety valve 32A to interconnect the fuel from thechamber 17A of the control device 15A to the main burner means 11A alsointerconnects fuel through the conduit 67A to the chamber 64A of theswitch construction 57A whereby even though the fuel pressuredifferential across the diaphragm 61A is now equal, the force of thecompression spring 78A is greater than the natural resiliency of thespring blade 72A so that the diaphragm 61A is moved upwardly in themanner illustrated in FIG. 2 to open the switch 68A and terminate theoperation of the unit 43A.

The safety valve 32A continues to supply fuel to the burner means 11A aslong as the valve member 22A is in an open condition. However, when thebulb 26A senses that the temperature of the oven 12A is at or slightlyabove the temperature setting of the selector means 14A, the powerelement 24A has expanded to such an extent that the same closes thevalve member 22A against the valve seat 23A and the flow of fuel to thepilot burner means 28A is now terminated through the valve seat 23Awhereby if the bypass 30A is provided in the control device 15A, only asmall standby flame will exist at the pilot burner means 28A.

Subsequently, should the temperature of the oven fall I below theselected temperature, the valve member 22A is again moved away from thevalve seat 23A and sufficient fuel now entersthe chamber 87 of theelectrical switch construction 57A to combine with the force of thespring blade 72A to overcome the force of the compression spring 78A andmove the switch blade 72A to a closed position so that the ignitor 43Awill again be operated to ignite the fuel issuing from the pilot burnermeans 28A at the end 40A thereof if the standing pilot flame thereofceases to exist or does not exist through elimination of the bypasspassage 30A as the case may be.

Thus, it can be seen that each time the heater pilot 28A is cycled on,the ignition unit 43A will be operated by the switch means 57A to insureignition thereof so that the valve means 32A can be moved to its opencondition to supply the fuel to the burner means 11A.

Of course, the springs 72A and 78A and the diaphragm 61A can be so sizedthat the diaphragm 71A will not be moved downwardly in FIG. 2 to closethe switch 68A when the valve member 22A is only moved partially awayfrom the valve seat 23A after the temperature of the oven has come tonear the selected temperature as in the system 10 previously describedwhereby the switch construction 57A will only cause the ignition unit43A to be operated at the start of a particular cycle of operation ofthe oven 12A in the manner provided by the system 10 previouslydescribed.

In any event, it can be seen that this invention provides an improvedfuel control system having ignition means that will only be renderedoperative during a selected use of the control system so that nostanding pilot flame is required for the system during nonuse of thesystem as in the control systems set forth in the aforementioned U.S.patents.

Thus, this invention not only provides an improved fuel control systembut also this invention provides an improved method of operating such acontrol system or having a pilot burner means therefor and athermostatically operated control device for directing fuel from asource thereof to said pilot burner means upon the demand of fuel forsaid main burner means whereby a safety valve will direct fuel from saidsource to said main burner means only upon the detection of a certainflame means at said pilot burner means, the improvement whereinelectrical ignition means is provided for igniting fuel issuing fromsaid pilot burner means, and a condition responsive device is providedfor rendering said ignition means operable when fuel is directed to saidpilot burner means upon a demand for fuel for said main burner means'bysaid condition responsive device being responsive to said fuel flow tosaid pilot burner means and for rendering said ignition means inoperablewhen said safety valve is directing fuel from said source to said mainburner means upon a detection thereby of said certain flame means atsaid pilot burner means by said condition responsive device beingresponsive to said fuel flow to said main burner means.

2. In a fuel control system as set forth in claim l,said conditionresponsive device rendering said ignition means so operable and theninoperable each time said fuel is directed to said pilot burner means bysaid control device upon said demand for fuel for said main burnermeans.

3. In a fuel control system as set forth in claim 1, said conditionresponsive device rendering said ignition means so operable-and theninoperable substantially only at the start of a cycle of operation ofsaid main burner means as set by said control device.

4. In a fuel control system as set forth in claim 1, said pilot burnermeans being a dual rate pilot burner means whereby said system has meansfor directing a standby flow of fuel from said source to said pilotburner means to produce a standby flame means at said pilot burner meansthat is not detected by said safety valve means.

5. In a fuel control system as set forth in claim 4, said control devicehaving means for terminating said flow of fuel to said pilot burnermeans when said control device is disposed in an of condition thereof.

6. In a fuel control system as set forth in claim 1, said conditionresponsive device comprising a diaphragm operated electrical switchconstruction for interconnecting an electrical power source to saidignition means when an electrical switch of said construction is closed.

7. In a fuel control system as set forth in claim 6, said diaphragmswitch construction having a single diaphragm operatively controllingsaid switch, said construction having means for imposing pilot burnermeans fuel flow pressure on one side of said diaphragm to tend to closesaid switch and having means for imposing main burner means fuel flowpressure on the other side of said diaphragm to tend to open saidswitch.

8. In a fuel control system as set forth in claim 7, said switchconstruction having biasing means operatively acting on said switch in adirection to normally maintain said switch in an open condition thereof.

9. In a fuel control system as set forth in claim 6, said diaphragmswitch construction having a pair of diaphragms operatively controllingsaid switch, said construction having means for imposing pilot burnermeans fuel flow pressure on one side of one of said diaphragm to tend toclose said switch and having means for imposing main burner means fuelflow pressure on one side of the other of said diaphragms to tend toopen said switch.

10. In a fuel control system as set forth in claim 9, said diaphragmswitch construction having means for directing source fuel pressurebetween said diaphragms to respectively act on the other sides thereofto tend to maintain said switch in the open conditions thereof.

11. In a fuel control system for a main burner means having a pilotburner means therefor and a manually settable thermostatically operatedcontrol device for directing fuel from a source thereof to said pilotburner means upon the demand of fuel for said main burner means wherebya safety valve will direct fuel from said source to said main burnermeans only upon the detection of a certain flame means at said pilotburner means so that said safety valve will be cycled on and of to tendto maintain the output temperature effect of said main burner means atthe particular setting of said control device, the improvement whereinan electrical ignition means is provided for igniting fuel issuing fromsaid pilot burner means, and for rendering said ignition means operablesubstantially only when fuel is initially directed to said pilot burnermeans upon a demand for fuel for said main burner means caused by aninitial setting of said control from an of condition thereof to adesired on" condition thereof and for thereafter rendering said ignitionmeans inoperable for that particular setting of said control device whensaid safety valve is initially directing fuel from said source to saidmain burner means upon a detection thereby of said certain flame meansat said pilot burner means even though said safety valve is subsequentlycycled on" and of during that particular setting of said control devicev12. In a fuel control system as set forth in claim 11, said pilot burnermeans being a dual rate pilot burner means whereby said system has meansfor directing a standby flow of fuel from said source to said pilotburner means to produce a standby flame means at said pilot burner meansthat is not detected by said safety valve means.

13. In a fuel control system as set forth in claim 12, said controldevice having means for terminating said flow of fuel to said pilotburner means when said control device is disposed in an off" conditionthereof.

14. In a fuel control system as set forth in claim 1, said means foroperating said ignition means comprising a diaphragm operated electricalswitch construction for interconnecting an electrical power source tosaid ignition means when an electrical switch of said construction isclosed.

15. In a fuel control system as set forth in claim 14, said diaphragmswitch construction having a pair of diaphragms operatively controllingsaid switch, said construction having means for imposing pilot burnermeans fuel flow pressure on one side of one of said diaphragms to tendto close said switch and having means for imposing main burner meansfuel flow pressure on one side of the other of said diaphragms to tendto open said switch.

16. In a fuel control system as set forth in claim 15, said diaphragmswitch construction having means for directing source fuel pressurebetween said diaphragms to respectively act on the other sides thereofto tend to maintain said switch in the open condition thereof.

17. In a method of operating a fuel control system for a main burnermeans having a pilot burner means therefor and a thermostaticallyoperated control device for directing fuel from a source thereof to saidpilot burner means upon the demand of fuel for said main burner meanswhereby a safety valve will direct fuel from said source to said mainburner means only upon the detection of a certain flame means at saidpilot burner means, the improvement comprising the steps of providing anelectrical ignition means for igniting fuel issuing from said pilotburner means, providing a condition responsive device, rendering saidignition means operable with said condition responsive device when fuelis directed to said pilot burner means upon a demand for fuel for saidmain burner means by causing said condition responsive device to beresponsive to said fuel flow to said pilot burner means, and renderingsaid ignition means inoperable with said condition responsive devicewhen said safety valve is directing fuel from said source to said mainburner means upon a detection thereby of said certain flame means atsaid pilot burner means by causing said condition responsive device tobe responsive to said fuel flow to said main burner means.

18. In a method as set forth in claim 17, the additional step of causingsaid condition responsive device to render said ignition means sooperable and then inoperable each time said fuel is directed to saidpilot burner means by said control device upon said demand for fuel forsaid main burner means.

19. In a method as set forth in claim 17, the additional step of causingsaid condition responsive device to render said ignition means sooperable and then inoperable substantially only at the start of a cycleof operation of said main burner means as set by said control device.

20. In a method as set forth in claim 17, the additional step of formingsaid pilot burner means from a dual rate pilot burner means, anddirecting a standby flow of fuel from said source to said pilot burnermeans to produce a standby flame means at said pilot burner means thatis not detected by said safety valve means.

21. In a method as set forth in claim 20, the additional step of formingsaid control device with means for terminating said flow of fuel to saidpilot burner means when said control device is disposed in an ofcondition thereof.

22. In a method as set forth in claim 17, the additional step of formingsaid condition responsive device from a diaphragm operated electricalswitch construction for interconnecting an electrical power source tosaid ignition means when an electrical switch of said construction isclosed.

23. In a method as set forth in claim 22, the additional steps offorming said diaphragm switch construction with a single diaphragmoperatively controlling said switch, imposing pilot burner means fuelflow pressure on one side of said diaphragm to tend to close saidswitch, and imposing main burner means fuel flow pressure on the otherside of said diaphragm to tend to open said switch.

24. In a method as set forth in claim 23, the additional step of formingsaid switch construction with biasing means for operatively acting onsaid switch in a direction to normally maintain said switch in an opencondition thereof.

25. In a method as set forth in claim 22, the additional steps offorming said diaphragm switch construction with a pair of diaphragmsoperatively controlling said switch, imposing pilot burner means fuelflow pressure on one side of one of said diaphragms to tend to closesaid switch, and imposing main burner means fuel flow pressure on oneside of the other of said diaphragms to tend to open said switch.

26. In a method as set forth in claim 25, the additional step ofdirecting source fuel pressure between said diaphragms to respectivelyact on the other sides thereof to tend to maintain said switch in theopen condition thereof.

27. In a method for operating a fuel control system for a main burnermeans having a pilot burner means therefor and a manuallly settablethermostatically operated control device for directing fuel from asource thereof to said pilot burner means upon the demand of fuel forsaid main burner means whereby a safety valve will direct fuel from saidsource to said main burner means only upon the detection of a certainflame means at said pilot burner means so that said safety valve will bycycled on and of to tend to maintain the output temperature effect ofsaid main burner means at the particular setting of said control device,the improvement comprising the steps of providing an electrical ignitionmeans for igniting fueliiissuring from said pilot burner means,rendering said ignition means operable substantially only when fuel isinitially directed to said pilot burner means upon a demand for fuel forsaid main burner means caused by an initial setting of said control froman of condition thereof to a desired on condition thereof and thereafterrendering said ignition means inoperabale for that particular setting ofsaid control device when said safety valve is initially directing fuelfrom said source to said main burner means upon a detection thereby ofsaid certain flame means at said pilot burner means even though saidsafety valve is subsequently cycled on" and off" during that particularsetting of said control device.

28. In a method as set forth in claim 27, the additional steps offorming said pilot burner means from a dual rate pilot burner means, anddirecting a standby flow of fuel from said source to said pilot burnermeans to produce a standby flame means at said pilot burner means thatis not detected by saidsafety valve means.

29. In a method as set forth in claim 28, the additional step of formingsaid control device with means for terminating said flow of fuel to saidpilot burner means when said control device is disposed in an off"condition thereof.

30. [n a method as set forth in claim 27, the additional step ofproviding means for operating said ignition means from a diaphragmoperated electrical switch construction for interconnecting anelectrical power source to said ignition means when an electrical switchof said construction is closed.

31. In a fuel control system as set forth in claim 30, the additionalsteps of forming said diaphragm switch construction with a pair ofdiaphragms operatively controlling said switch, imposing pilot burnermeans fuel flow pressure on one side of one of said diaphragms to tendto close said switch, and imposing main burner means fuel flow pressureon one side of the other of said diaphragms to tend to open said switch.

32. In a method as set forth in claim 31, the additional step ofdirecting source fuel pressure between said diaphragms to respectivelyact on the other sides thereof to tend to maintain said switch in theopen con dition thereof.

1. In a fuel control system for a main burner means having a pilotburner means therefor and a thermostatically operated control device fordirecting fuel from a source thereof to said pilot burner means upon thedemand of fuel for said main burner means whereby a safety valve willdirect fuel from said source to said main burner means only upon thedetection of a certain flame means at said pilot burner means, theimprovement wherein electrical ignition means is provided for ignitingfuel issuing from said pilot burner means, and a condition responsivedevice is provided for rendering said ignition means operable when fuelis directed to said pilot burner means upon a demand for fuel for saidmain burner means by said condition responsive device being responsiveto said fuel flow to said pilot burner means and for rendering saidignition means inoperable when said safety valve is directing fuel fromsaid source to said main burner means upon a detection thereby of saidcertain flame means at said pilot burner means by said conditionresponsive device being responsive to said fuel flow to said main burnermeans.
 2. In a fuel control system as set forth in claim 1, saidcondition responsive device rendering said ignition means so operableand then inoperable each time said fuel is directed to said pilot burnermeans by said control device upon said demand for fuel for said mainburner means.
 3. In a fuel control system as set forth in claim 1, saidcondition responsive device rendering said ignition means so operableand then inoperable substantially only at the start of a cycle ofoperation of said main burner means as set by said control device.
 4. Ina fuel control system as set forth in claim 1, said pilot burner meansbeing a dual rate pilot burner means whereby said system has means fordirecting a standby flow of fuel from said source to said pilot burnermeans to produce a standby flame means at said pilot burner means thatis not detected by said safety valve means.
 5. In a fuel control systemas set forth in claim 4, said control device having means forterminating said flow of fuel to said pilot burner means when saidcontrol device is disposed in an ''''off'''' condition thereof.
 6. In afuel control system as set forth in claim 1, said condition responsivedevice comprising a diaphragm operated electrical switch constructionfor interconnecting an electrical power source to said ignition meanswhen an electrical switch of said construction is closed.
 7. In a fuelcontrol system as set forth in claim 6, said diaphragm switchconstruction having a single diaphragm operatively controlling saidswitch, said construction having means for imposing pilot burner meansfuel flow pressure on one side of said diaphragm to tend to close saidswitch and having means for imposing main burner means fuel flowpressure on the other side of said diaphragm to tend to open saidswitch.
 8. In a fuel control system as set forth in claim 7, said switchconstruction having biasing means operatively acting on said switch in adirection to normally maintain said switch in an open condition thereof.9. In a fuel control system as set forth in claim 6, said diaphragmswitch construction having a pair of diaphragms operatively controllingsaid switch, said construction having means for imposing pilot burnermeans fuel flow pressure on one side of one of said diaphragm to tend toclose said switch and having means for imposing main burner means fuelflow pressure on one side of the other of said diaphragms to tend toopen said switch.
 10. In a fuel control system as set forth in claim 9,said diaphragm switch cOnstruction having means for directing sourcefuel pressure between said diaphragms to respectively act on the othersides thereof to tend to maintain said switch in the open conditionsthereof.
 11. In a fuel control system for a main burner means having apilot burner means therefor and a manually settable thermostaticallyoperated control device for directing fuel from a source thereof to saidpilot burner means upon the demand of fuel for said main burner meanswhereby a safety valve will direct fuel from said source to said mainburner means only upon the detection of a certain flame means at saidpilot burner means so that said safety valve will be cycled ''''on''''and ''''off'''' to tend to maintain the output temperature effect ofsaid main burner means at the particular setting of said control device,the improvement wherein an electrical ignition means is provided forigniting fuel issuing from said pilot burner means, and for renderingsaid ignition means operable substantially only when fuel is initiallydirected to said pilot burner means upon a demand for fuel for said mainburner means caused by an initial setting of said control from an''''off'''' condition thereof to a desired ''''on'''' condition thereofand for thereafter rendering said ignition means inoperable for thatparticular setting of said control device when said safety valve isinitially directing fuel from said source to said main burner means upona detection thereby of said certain flame means at said pilot burnermeans even though said safety valve is subsequently cycled ''''on''''and ''''off'''' during that particular setting of said control device.12. In a fuel control system as set forth in claim 11, said pilot burnermeans being a dual rate pilot burner means whereby said system has meansfor directing a standby flow of fuel from said source to said pilotburner means to produce a standby flame means at said pilot burner meansthat is not detected by said safety valve means.
 13. In a fuel controlsystem as set forth in claim 12, said control device having means forterminating said flow of fuel to said pilot burner means when saidcontrol device is disposed in an ''''off'''' condition thereof.
 14. In afuel control system as set forth in claim 1, said means for operatingsaid ignition means comprising a diaphragm operated electrical switchconstruction for interconnecting an electrical power source to saidignition means when an electrical switch of said construction is closed.15. In a fuel control system as set forth in claim 14, said diaphragmswitch construction having a pair of diaphragms operatively controllingsaid switch, said construction having means for imposing pilot burnermeans fuel flow pressure on one side of one of said diaphragms to tendto close said switch and having means for imposing main burner meansfuel flow pressure on one side of the other of said diaphragms to tendto open said switch.
 16. In a fuel control system as set forth in claim15, said diaphragm switch construction having means for directing sourcefuel pressure between said diaphragms to respectively act on the othersides thereof to tend to maintain said switch in the open conditionthereof.
 17. In a method of operating a fuel control system for a mainburner means having a pilot burner means therefor and a thermostaticallyoperated control device for directing fuel from a source thereof to saidpilot burner means upon the demand of fuel for said main burner meanswhereby a safety valve will direct fuel from said source to said mainburner means only upon the detection of a certain flame means at saidpilot burner means, the improvement comprising the steps of providing anelectrical ignition means for igniting fuel issuing from said pilotburner means, providing a condition responsive device, rendering saidignition means operable with said condition responsive device when fuelis directed to said pilot burner means upon a demand for fuel for saidmain burner meAns by causing said condition responsive device to beresponsive to said fuel flow to said pilot burner means, and renderingsaid ignition means inoperable with said condition responsive devicewhen said safety valve is directing fuel from said source to said mainburner means upon a detection thereby of said certain flame means atsaid pilot burner means by causing said condition responsive device tobe responsive to said fuel flow to said main burner means.
 18. In amethod as set forth in claim 17, the additional step of causing saidcondition responsive device to render said ignition means so operableand then inoperable each time said fuel is directed to said pilot burnermeans by said control device upon said demand for fuel for said mainburner means.
 19. In a method as set forth in claim 17, the additionalstep of causing said condition responsive device to render said ignitionmeans so operable and then inoperable substantially only at the start ofa cycle of operation of said main burner means as set by said controldevice.
 20. In a method as set forth in claim 17, the additional step offorming said pilot burner means from a dual rate pilot burner means, anddirecting a standby flow of fuel from said source to said pilot burnermeans to produce a standby flame means at said pilot burner means thatis not detected by said safety valve means.
 21. In a method as set forthin claim 20, the additional step of forming said control device withmeans for terminating said flow of fuel to said pilot burner means whensaid control device is disposed in an ''''off'''' condition thereof. 22.In a method as set forth in claim 17, the additional step of formingsaid condition responsive device from a diaphragm operated electricalswitch construction for interconnecting an electrical power source tosaid ignition means when an electrical switch of said construction isclosed.
 23. In a method as set forth in claim 22, the additional stepsof forming said diaphragm switch construction with a single diaphragmoperatively controlling said switch, imposing pilot burner means fuelflow pressure on one side of said diaphragm to tend to close saidswitch, and imposing main burner means fuel flow pressure on the otherside of said diaphragm to tend to open said switch.
 24. In a method asset forth in claim 23, the additional step of forming said switchconstruction with biasing means for operatively acting on said switch ina direction to normally maintain said switch in an open conditionthereof.
 25. In a method as set forth in claim 22, the additional stepsof forming said diaphragm switch construction with a pair of diaphragmsoperatively controlling said switch, imposing pilot burner means fuelflow pressure on one side of one of said diaphragms to tend to closesaid switch, and imposing main burner means fuel flow pressure on oneside of the other of said diaphragms to tend to open said switch.
 26. Ina method as set forth in claim 25, the additional step of directingsource fuel pressure between said diaphragms to respectively act on theother sides thereof to tend to maintain said switch in the opencondition thereof.
 27. In a method for operating a fuel control systemfor a main burner means having a pilot burner means therefor and amanuallly settable thermostatically operated control device fordirecting fuel from a source thereof to said pilot burner means upon thedemand of fuel for said main burner means whereby a safety valve willdirect fuel from said source to said main burner means only upon thedetection of a certain flame means at said pilot burner means so thatsaid safety valve will by cycled ''''on'''' and ''''off'''' to tend tomaintain the output temperature effect of said main burner means at theparticular setting of said control device, the improvement comprisingthe steps of providing an electrical ignition means for igniting fuelissuring from said pilot burner means, rendering said ignition meansoperable substantiallY only when fuel is initially directed to saidpilot burner means upon a demand for fuel for said main burner meanscaused by an initial setting of said control from an ''''off''''condition thereof to a desired ''''on'''' condition thereof andthereafter rendering said ignition means inoperabale for that particularsetting of said control device when said safety valve is initiallydirecting fuel from said source to said main burner means upon adetection thereby of said certain flame means at said pilot burner meanseven though said safety valve is subsequently cycled ''''on'''' and''''off'''' during that particular setting of said control device. 28.In a method as set forth in claim 27, the additional steps of formingsaid pilot burner means from a dual rate pilot burner means, anddirecting a standby flow of fuel from said source to said pilot burnermeans to produce a standby flame means at said pilot burner means thatis not detected by said safety valve means.
 29. In a method as set forthin claim 28, the additional step of forming said control device withmeans for terminating said flow of fuel to said pilot burner means whensaid control device is disposed in an ''''off'''' condition thereof. 30.In a method as set forth in claim 27, the additional step of providingmeans for operating said ignition means from a diaphragm operatedelectrical switch construction for interconnecting an electrical powersource to said ignition means when an electrical switch of saidconstruction is closed.
 31. In a fuel control system as set forth inclaim 30, the additional steps of forming said diaphragm switchconstruction with a pair of diaphragms operatively controlling saidswitch, imposing pilot burner means fuel flow pressure on one side ofone of said diaphragms to tend to close said switch, and imposing mainburner means fuel flow pressure on one side of the other of saiddiaphragms to tend to open said switch.
 32. In a method as set forth inclaim 31, the additional step of directing source fuel pressure betweensaid diaphragms to respectively act on the other sides thereof to tendto maintain said switch in the open condition thereof.